I. Field of the Invention
This invention relates to a mechanism for determining the margins for a sheet of paper in a typewriter, and more particularly to a carrier mounted sensor and associated apparatus and circuitry for determining the width of the sheet of paper and for setting margins of a predetermined width.
II. Prior Art
Heretofore, the setting of margins for a sheet of paper has been left almost entirely to the skill and judgement of the typist. For standard size paper, this does not present a problem. However, if variable widths of paper are used, margins as numerous as the sheet widths may result.
In the prior art there are teachings of preprogrammed margins and tab racks. For example, U.S. Pat. No. 3,020,996 discloses an optical sensing mechanism for sensing marks on the sheet to control tab position settings. This patent further provides for mechanically settable margins. U.S. Pat. No. 3,785,471 teaches the automatic setting of left and right margins in accordance with the position of a center point indicator so that the margin stops are positioned by movement of the pointer to correspond to the margins required for a particular letter size (e.g., the number of words in the letter). While a form of sensing is disclosed by one reference and the teaching of automatic margin setting is disclosed in another, sheet width sensing and automatic margin setting in accordance with this sensed width is not disclosed in the prior art.
It is known in the prior art to utilize the sensed size of a sheet to control machine function. Exemplary of patents teaching this type of application is U.S. Pat. No. 3,809,472 which discloses a xerographic device in which the size of sheet being transported through a xerographic copier is sensed in order to control the exposure given the side portions of a photoconductive drum. In effect, the photoconductive drum is charged by an amount determined by the width of the sheet to be utilized in the copy machine.
Again, none of the prior art teaches the concept of sensing the sheet width in order to automatically control the setting of margins in a typewriter mechanism.